One of the most important and challenging aspects of software development is testing. Testing involves determining whether software executes in a manner consistent with the software's intended behavior. The software's intended behavior may be defined using an executable specification language such as the Abstract State Machine Language (AsmL). AsmL may be employed to specify precise conforming behavior (a deterministic specification), or to specify ranges or choices within which various acceptable behaviors may take place (a non-deterministic specification). Non-deterministic specifications are desirable because they do not specify the implementation behavior down to the finest detail. Non-deterministic specifications define choices for behavior, allowing the software implementer design freedom within those choices. An AsmL specification may be executed by itself (in a stand-alone manner) or in conjunction with a separate implementation in order to ascertain whether or not the behavior defined by the specification is in fact the desired behavior.
A software implementation's runtime behavior may be compared against the specified behavior to identify non-conformities. This process is referred to as conformance testing. One approach to conformance testing is to insert code into the software to test conditions. The conditions define the desired state of the software at method boundaries of the software. For examples of this approach, see Bertrand Meyer, Eiffel: The Language, Object Oriented Series, Prentice Hall, New York, N.Y., 1992. See also the White Paper by Murat Karaorman et al. of Texas Instruments et al., entitled jContractor: A Reflective Java Library to Support Design By Contract, and the White Paper by Reto Kramer of Cambridge Technology Partners, entitled iContract—The Java Design by Contract Tool. 
A limitation of existing methods of conformance testing is that they do not provide adequate support for non-deterministic specifications. Another limitation of existing methods is that they do not adequately address the conformance checking of call sequences. A software specification may indicate that processing within a method of an implementing class should proceed in steps, e.g. in a particular order. The specification may also indicate that the implementation method must make calls to methods of another class (so called ‘mandatory calls’). The mandatory calls may lead to re-entrance of methods of the implementing class, resulting in unpredictable state changes while the mandatory calls are still pending. Existing approaches to conformance checking do not adequately address this situation.